Alternating current television



Jan. 5, 1932. c NlCOLSON 1,839,696

ALTERNATING CURRENT TELEVISION Filed May 5, 1950 2 Sheets-Shet 1 EQUELL INVENTOR A/exanaer M 1640 Mbolson.

ATTORNEY Jan. 5, 1932- A. MGL. NICOLSON ALTERNATING CURRENT TELEVISION Filed May 5, 1930 2 Sheets-Sheet 2 Han INVENTOR A/exanaer M Lean N/co/son.

J/KW ATTORNEY Patented Jan. 5, 1932 UNITED STATES PATENT OFFICE ALEXANDER MGLEANi NICOLSON, OF NEW YORK N.'Y., ASSIGNOR TO COMMUNICATION PATENTS} INQ, OF NEW -YORK, N. Y., A CORPORATION E DELAWARE ALTERNATING CURRENT TELEVISION Applieation flled May 5,- 1930. Serial No. 450,025.

This invention relates to the transmission and? reception of intelligence over wires or through space, and particularly to the transmission and reception of images as in a television system.

In the transmission of images or pictures it is necessary to illuminate the object in some manner. This may be accomplished by scanning the object with a point of light, the reflection or projection. of which w1ll register the relative densities of light and shade ofthe object on a photoelectric cell. These relative densities of light Will be transformed into corresponding electrical variations by means of the photoelectric cell which variations may be transmitted to'receiving apparatus. It is well known that if these light variations are reproducedbefore the eye at the rate" of cycles per second or faster, they will appear as a picture of the object scanned by the transmitter. I

In my copending application Ser. No.

397,826, filed October 7, 1929, a system for the simultaneous transmission and reception of successive unit portions of a scene has been disclosed. I In this application an arc traveling at a high rate of speed between two polarized electrode rails in a magnetic field is employed as the scanning and reception medium. As this are illuminates unit areas ofthe scene to be transmitted, reflected light from the scene or object is, impressed on a,

photoelectric cell and transformed into ele c-I I trical vibrations. In the system disclosed f 1 in this copendingiapplication, directcurrent energy is used to energize the fields and direct current potential diiferences to maintain the traveling arc. alternating currents are employed as the sole energy sources. I

An object of this invention is 'to accomplish television with transmitting and receiving apparatus containing no moving parts whatsoever.

Another object of the invention is to transmit and receive images electrically Withapparatus supplied from a single'alternating current energy source.

I A further object of the invention is to ob- In the present invention tain absolute synchrony of transmission and reception. I

A. still further object of the invention is to obtain a uniform scanning speed during fluctuations of the energy source.

A feature of the present invention is the arrangement of thearc and driving fields in.

series and/or in parallel and supplied from asingle alternating current source of comparatively high frequency so that reversals of the field magnetism is accompanied by a reversal of polarity of the arc electrodes, maintaining, therefore, a continuous are so far as the eye is aware.

I Another feature of the invention is the maintaining of a substantially constant driving force for the arc during variations, or fluctuations of the alternating current voltage supply by means of differential windings in a series parallel relationship with the main field winding and the electrodes of the scanchronizing circuit for the transmitter and receiv ng apparatus in Figs. land 2; and

Figs. 4 and 5 are. diagrammatic drawings of the power supply for the circuits in the embodiment of the inventionshown in Figs. land2. I I

QBeferring to the drawings, and particularly to. Fig. 1,. transmission apparatus is sho wnfin accordance with the invention.

passes through a pinhole 7 in the camera 8,

Fig. 3 is a schematic drawing ofthe syn- ,Endless electrode rails 5 and 6 are shown in I ing from the point 12, a diflerential winding 13 is shown in series with the arc and main field winding but wound in the reverse direction to that of the main field winding and terminating at point 15. It is to be understood, however, that the main field winding ma be in shunt to the energysource and the di erential winding in series with the are or vice versa, regulation being accomplished with the aid of the are characteristic. The are electrodes 5 and 6 and the two field windings 11 and 13 are supplied with alternating current energy from a master oscillator 16 through the feeders 17 and 18. The master oscillator 16 in addition to supplying alternating current to energize the field and to maintain the arc, further supplies to the elements just mentioned piloting impulses for initiating the arc and framing the image and intermediate impulses which may have a lower amplitude than the piloting impulses. This function of the master oscillator is explained fully in my copending application mentioned above.

As the arc travels from the foreshortened gap 10 over the system horizontally, as shown by the configuration of the scanning screen electrodes, light projected to the object being scanned through pinhole 7 is reflected upon a photoelectric cell 20 or plurality of cells which may be located around the periphery of the screen. Variations in the light falling on the photoelectric cell due to the varying intensities of light and shade between unit areas of the object, are transformed into electrical variations corresponding thereto and impressed upon an amplifier 21 which increases their amplitude to the desired degree.

These current variations corresponding to the light fluctuations are impressed over conductors 23 on a modulator oscillator 22 in which they modulate a carrier wave for transmitting over an antenna system 24. The amplifier 21 and modulator oscillator 22 may be of any well known type. The an: tenna system 24 may be replaced by a wire system. I a

The master oscillator 16 has its frequency maintained constant by the use of a crystal control 26 which may have its temperature gulated to maintain its frequency substantially constant.

The transmitter also comprises a synchronizer 28 which has two inputs, one from the master oscillator through conductors 29, and the other from the electrode'rail 5 and probes 31 over conductors 30. It will be seen from pose of impressing on the latter the synchronizing and intermediate impulses for transmittal to the receiver for the purpose of maintaining perfect synchrony between the scanning are at the transmitter and the are at the receiver.

Referring now to Fig. 2, the elements shown in the receiving apparatus corresponding to the elements in the transmitting apparatus (Fig. 1) have been indicated by the same numerals with prime indicators. It is to be understood, of course, that the trans-' mitter and receiver may be adapted to alternate in function by the duplication of apparatus as disclosed in the above mentioned copending application but which is eliminated in the present disclosure for the purpose of clearness, as 'it forms no part of the present invention.

The transmitted picture modulations together with the arc currents and the piloting and intermediate.synchronizing impulses are received on an antenna system 40 and by detection at the receiver 41 are reduced to the original frequencies impressed on the modulator oscillatory system 22 from the photoelectric cell 20, amplifier 21 and the master oscillator 16. Certain of these frequencies namely the image components from derstood that filters of the band pass type or of the low frequenc or high frequency cutoff type may be use for segregating the picture component frequencies from the arc and Hpiloting frequencies dependin upon the 'auxiliary frequencies employe The are currents and the piloting and synchronizing impulses after amplification by amplifier 43 are impressed on the differential winding 13, main winding 11 and electrode rails 5 and 6' over conductors 18' and 17 Variations of light intensity are provided by the varying intensity of the are as it travels from the foreshortene'd gap 10 of the receiver over the electrode rails roducing an image of the object scanned y the apparatus in Fig. 1. In the present receiving apparatus, itwill be observed that a synchronizer 28, a replica of the synchronizer 28 in Fig. 1, is connected to the probe at theforeshortened gap 10' probes 31 over conductors 30' and to the receiver over conductors 29. A full wave rectifica- J29 tion system which may be of either the chemical or electron tube type, is shown, the purpose thereof to be explained later.

In Fig. 3 is shown a schematic circuit of the synchronizers 28 and 28 of Figs. 1 and 2. Two tubes and 51 are connected in a push pull bridge circuit with a common plate supply 52. The input of tube 50 is from either of the probes atthe foreshortened gaps 10 and 10 and the respective probes 31 and 31, these probes beingpositioned in the path of the are but insulated from the rails. Assuming for explanatory purposes that the synchronizer circuit of Fig. 3 is synchronizer 28 (Fig. 1), electrode rail 5 and probes 31 are shown in the input of tube 50. The input of tube 51 is shown connected to the master oscillator 16, which will be replaced by the output of the receiver 41 in the system of Fig. 2. The synchronizing circuit further comprises two rectifiers 54 and 56 which are for thepurpose of supplying a direct current i bias for the respective tubes. Therectifier 56 is effectively connected in the plate circuit of tube 50 through a transformer 57 and the rectifier 54 is effectively connected in the late circuit of tube. 51 through a transormer 58. The output circuits of tubes 50 and 51 are connected to the input circuits of a balanced tube systein 60'through the transformers '61 and 62, respectively. Intermediate the output circuit of tube-51 and one of the input circuits of the system 60 is a transformer 63 for shifting the phase of the output currents from this tube 180 degrees. In the inputs of the tubes 50 and 51 are series resistances 69 and 76 for the purpose of controlling the amplitudes of the incoming impulses. Resistance 69 also offers a high impedance across the arc rails.

- The system 60 comprises twovacuum tubes .64 and 65 having a common anode energy supply 66 in series with the primary of an output transformer 67. The transformer 67 feeds an amplifier system which in turn is connected tothe auxiliarycontrolszintling 33 the winding 68 being'the primary of the transformer 34.

y In Figs. 4 and 5, a diagrammatic representation is made of power distribution systems for the yacuumtubes of. the amplifiers, oscillators, modulators and synchronizer circuits.

Ordinary power sources shown at 70 and 71, which may be either single or polyphase, are connected to rectification systems 72 and 73 for source 70, and rectification systems 74 and 75 for source 71. These systems. may be coupled by transformers 77 and 78, respectively. Since the result of rectification is not generally a pure direct current, but contains alternating components which may interfere with the transmission of the image current components, filters- 80, 81, 82 and 83 are employed to. eliminate these deleterious ripples. Theelements requiring'powermay be tapped ofi as shown by otentiometers 85, 86 and 87 for the system in ig. 4, and potentiometers 88, 89, 90, 91, 92 and '93 for the systemin Fig. 5-. The output leads from the filters may be of difi'erent voltages. Itmay be desirable in these rectification systems to employ floating storage batteries as shown at 95, 96 and 97, for the purpose of steadying the energy supply to the various loads, since the satisfactory operation of the system depends to a certain extent upon the constancy of the voltage from the supply so-urces.'

The operation of the, system referred to in Fig. 1-is as follows: A potential difference is impressed across the rails 5 and 6 .over conductors 17 and 18 and windings 11 and 13 of suflicient amplitude to initiate an arc. Y

Then the arc forms, current will flow in a certain direction through the main field windings 11 and differential field windings 13 inaccordance with the polarity of the electrode'rails. As the field winding 11 has a' preponderance of turns over that of winding 13, there is a differential flux forming a pole in which the are at the gap 10 is located. The presence of the arc in the field causes a force to be exerted on the are which drives it along the electrode rails 5 and 6. Since the source is alternating, however, the arc will be driven only a certain distance under these conditionsthat is, during one half cycle of the supply frequency. However, at the reversal of polarity of the electrodes during the next half cycle, it is obvious that the field will also reverse in. polarity, furnishing a driving force in the same direction during thishalf cycle causing the arc to traverse the scanning field always in the same direction.

Analogously, by changing both the field and armature leads to a motor, no change in direction of rotation is made. The initiating half cycle of the supply frequency may be of greater amplitude than the remainder of'the wave, rcinitiation of the arc being possible at each half cycle because of the immediate previous ionization which permits the arc to form at a lower amplitude. These alternations arev at a sufiiciently high frequency that any disappearance of the arc at the nodal points is not perceptible to the eye.

Now if for any reason the supply potential rises, the main field 11 will naturally strengthen due to the increased flow of current therethrough, tending to cause a faster motion to the are over its scanning rails. Strengthening of the'ma-in field, however, is substantially eliminated,because the correspondingincrease in field strength of the differential windings 13 neutralizes the increase of flux caused by the main winding. The reverse. action occurs when the supply voltage drops. In this manner, therefore, constant cyclic speed forthe are over the scanning rails is obtained by use of the differential action of these field windings. i

To further obtain constant arc scanning speed'the synchronizer 28 is employed in the same manner as that used in t e s stem of my copending application above re erred to.

5 However, a brief description thereof will be made here to account for any; change in detail.

Referring to Figs. 1 and 3 simultaneously, a piloting impulse which is actually one half cycle of the supply frequency having a high amplitude, serves to initiate the are on both the transmitter and receiver screens. These piloting impulses, therefore, accomplish the framing of the image, and provide the tim- 1 ing element required for scanning at the transmitter'and for synchronous reception of the image at the receiver. Furthermore,

. these piloting impulses act to maintain a constant cyclic'speed of scanning over the entire 2 screen. They will be received in the input circuit of tube 50 over the conductors from the gap probe and at the sameinstant in the input circuit of tube 51 over conductors 29 directly from the master oscillator .164 If 25 corresponding impulses arrive at the synchronizer' at the same instant, no chan e will take placein the output circuits thereo ,s'ince .each tube. will block the action of the other by increasing the respective rid bias throu h the rectifiers 54 and 56. ven should the tubes increase their plate currents simultaneous'ly, no efi'ect-would occur in the system 60,

because of the equal value and opposite phase 3 reaches the shunts 31 at the proper time, these of the currents reaching system 60. However, if the arc has been advanced through undesirable influences during its travel over the scanning rails, and reaches the gap a trifle -in advanceof the succeeding impulse from the master oscillator, it will produce an imulse in the input of tube 50, and there will e no increased bias to prevent the functioning of tube as no counter impulse has arrived-at tube 51. Tube 50 willnow increase its .plate current to produce an increase in negative potential 'on the grid of the tube 51 through the rectifier 56, causing tube 51 to cease to function during operation of tube 50. The succeeding impulses will be received at the synchronizer inputs at the same-instant and will have no effect thereon. It .will be understood that the la or advance is only a portion of a cycle, t e correction beingmade'during the half cycle. The impulse from the advanced arc will be of the base frequency and in phase with it, since it is produced b the are which in turn is produced by the asefrequency. The increase of plate current intube 5O unbalances system 60, is amplified in tube 64 and $0 imtpressed on thecontrol winding 33 in such a I rection as todecreasethe field in accord- .ance with the advance of the are at the foreshortened gap.- In this case the resulting' the main field current so as to weaken the field. This phase shift is obtained through the phase shifting properties of the transmisslon transformers. When the arc is lagging at the gap 10, and tube 51 receives an impulse from the master oscillator 16 before the ap probe impulse is impressed on tube 50, -t e impulse created by tube 51 is 180 out of phase with the impulse created by tube 50 but in phase with the main field current and consequently increases the field. This time element is accomplished by proportioning the frequency field strength and length of arc electrodes so'as to have an anti-node of the returning arc fall at the gap.

To obtain uniform cyclic propagation of the are over the screen, .the shunts 31 are employed. The master oscillator, as stated above furnishes intermediate impulses insuflicient to produce an arc in the gap 10, but

so. timed as to arrive at the synchronizer 28 over conductors 29 at the same instants that the main arc passes the shunts 31 which produce energy impulses in the input circuit of tube 50. These impulses are also so timed that an anti-node of the base frequency occurs when the arc is passing a 'probe at the proper time and at its right velocity. These interm'ediate impulses may be periodic half cycles of the supply frequency having an amplitude intermediate that of the piloting impulse and base current. Now' ifthe main are, traveling over the rails impulseswillneutralize those received from the master 'oscillator and no effect will be made upon the coiitrol winding 33 as in the case of the piloting impulses. However, if the arc is lagging or is in advance, then the one or the other of tubes 50 and 51 will be actuatedand the auxiliary field winding 33 will strengthened or' weakened in accordance thereto with the resultant speeding up or retardation of the traveling are. The action in System is exactly the same as in the case ofthe piloting impulses, the frequency thereof being the same. To ,obtain the proper phase of thecontrol currents-in its the winding 33, the frequency, field stren hand distancebetween shunts 31- is such t at the arc passesthe shunts at an anti-node of the supply frequency. The resistances p9 and 7 6 may be adjustai to obtain a zero difference between the amplitudes of the opposing waves the difference between the am litudes of the type of impulses being controiled at the master oscillaton It is to be understood that the piloting and synchronizing or intermediate impulses may be composed of harmonics of the base frequency, the em ployment of rectifiers then being necessary to produce the proper field-directional effects. the recelvingsystem of Fig. 2, there is a substantial d lication of the reactions occurring in thd hiaratus of Fig. 1. The

basic supply frequency with its piloting and. synchronizing impulsesis received from the I antenna together with the frequencies as the image of the object scanned. The wave shape of the piloting and intermediate impulses may be in the form of a sine wave but preferably of a peaked nature, in order to obtain a more sharp and positive action. By means of filter 46, the basic arc frequency- .is impressed -on amplifier 43 while by means of filter 44 only the photoelectric cell vibrations are impressed on amplifier 42 and rectifier 45. The basic arc frequency propagates the arc, the piloting impulses frame the image. and maintain a constant cyclic scanning speed, while the intermediate impulses maintain a uniform propagation of the are .over the image screen in-the same manner as in the transmitter :of Fig. 1 which has been explained above. However, currents corresponding to the light .and shade of the object are superimposed upon this arc to form the image. At certain periods during this superimposition, the photoelectric cellfrequencies and the arc frequency will be in phase and out of phase causing alternate fading and strengthening of portions of the images resulting in distortion thereof. This is corrected by the use of rectifier 45 which reverses half cycles of the photoelectric cell waves. Rectification when the currents are not in phase does not interfere withreception so that a rectifier may be placed in the circuit at all times. It is understood,-of course, that the amplitudes will not be comparable, but to eliminate any loss of definition in the pic-' ture, it is preferable to use the rectifier, although it is not always required. Furthermore, as in the system disclosed in my copending application mentioned above, the modulated carrier frequencies of the picture components may be I impressed directly on the screen electrodes without demodulation or rectification.

This embodiment of an alternating current transmission and receiving system has been shown with the arc and field in series but it is to be understood that the arc and the field may be placed in a parallel series relationship, the same reaction occurring as in a series relationship. When the polarity of therails is'chan ed, the polarity of the field is simultane'ous y changed and the travel of the arc is maintained in the same direction. Furthermore, other s nchronizing arrangements may be employe without departing from the spirit of this invention, and although the in- ,vention has been disclosed in one particular embodiment, it is understood that it is to be limited only by the scope of the appended 0 am.

prising, an electrodynamic arc screen, a field I claim: 4

1. A television transmission system comprising, an electrodynamic arc screen, a source of energy for said arc, a field for producing a driving force on said arc, means for transforming varying intensities of light into COI'r responding variations in electrical currents, and common supply means for said are and saidfield of an alternating character.

2. A television transmission system comwinding for said screen, acommon source of energy of an alternating character for said are and said field, means for transforming varying intensities of light into corresponding variations in electrical currents, and means for maintaining a substantially constant cyclic speed for said are during fluctuations in the common energy source.

3. A television transmission system comprising, an electrodynamic arc screen, a field for said screen, means for transforming varying'intensities of light into corresponding variations in electrical currents, and means for supplying said system solely from an alternating current source.

4. A television transmission system comprising an electrodynamic arc screen, a field winding supplying a flux for said screen, a common energy source for said are and said field winding of an alternating character, means for transforming varying intensities of light into corresponding variations in electrical currents, and means for varying the field of said are for maintaining the cyclic value of said field flux substantially constant;

5. A television system in accordance with claim 4, in which said means includes an auxiliary field windinililn series opposition with said first field win 6. An illuminating screen comprising a propagated arc in a magnetic field andeletrio rails for said screen forming adjacent arc,

paths, said arc and said magnetic field being supplied with alternating currents.

In a televlsion system, a transmitter scanning screen, means for initiating an electrodynamic arcand an arc. driving magnetic field insaid screen, a receiver. comprising a receiving screen and means controlled by said 1 rst means for initiating an electrodynamic arc and a magnetic field in [said receiver screen, said arcs and said fieldsbeing supplied with alternating curent.

8. In a' television system, a transmitter having a scanning screen, means for produc- 1ng an electrodynamic arc and an arc drlvlng magnetic field in said screen, a receiver comprising a receiver screen and means for profield in said receiver screen, and means controlled by said transmitter for synchronizing said arc, said arc and said field being supplied with alternating current.

9; In a television system, an electrody- 1 ducing an electrodynamic arc in a magnetic namic are screen including rail electrodes, a magnetic field for operating said are over said electrodes, an alternating current supply for said field, means for maintaining a substantially constant field during variations 11. A system in accordance with claim 10,

I in which said last-mentioned means includes means for controlling the propagation of said are in said magnetic field.

12. In a system for the transmission of electrical impulses corresponding to light variations defining an object, means for scanning said object including an electrodynamic are propa ated v along electrode rails in a magnetic eld, means for operating said scanning system with alternating current, and means for controlling the cyclic speed of said are and the propagation of said are in said magnetic field.

13. In a television scanning. system, a field coil producing a field flux, a rail electrode system positioned in said field, means for creating an arc between said electrode rails, said arc being propagated over said rails by said field flux, means for directing light from said are over objects in a two-dimensional pattern, and means for supplying said electrode rails and said field coils with alternating potentials.

14'. In a television scanning system,'a field coil producing a field flux, electrode rails positioned in said flux, an alternating potential onsaid electrode rails'and said field coils for producing a travelling arc along said rails, means positioned in the arc path at points atwhich an anti-node of the alternating supply potential occurs, and means for energizin a thermionic device with ener obtalne at said points, the output of sai thermionic device being utilized to. control the speed of said are.

1a. In a television system, a field coil producing a field flux in acertain direction, a secon field coil producing flux in-the opposite direction, one of said-coils producing a predominate flux, a rail electrode system positioned in the resultant field of said coils, means for creating an are between said electrode rails, said are being propagated through said field by said resultant flux,

-means for directing light,. from said are over objects whose images are to be transmitted, means for transforming the light and shade densities .over. said: obj ectinto corresponding electrical currents, andmeans for supplying said electrode rails and said field coils with alternating potentials.

16. In an electrical system, a field coil producing a field flux, a continuous rail electrode system positioned in said field, means for creatingan are between said electrode rails, a plurality of probes located in the path of said arc at equally spaced intervals along said are path, a thermionic device connected with said probes, a second thermionic device connected to a source of electric impulses, and means interconnecting said thermionic devices for determining the difference between the arrival of said are at said probes and the impression of said impulses on said second thermionic device'to vary the field flux of said system. 7

17. In a television transmission system, a difi'erential field coil producing a differential flux, a continuous elect-rode rail system positioned in said field, said. coils and said rails being supplied with alternating potentials, means for obtaining the light from said arc in a two dimensional pattern, means for detecting variations in said light and transforming said variations into electrical cur-' rents, means for transmitting said variations to a similar electrode rail system, means at said second rail system for generating impulses at definite time intervals, means for creating at said second screen a second plurality of impulses, and means for combining said impulses to change the field flux of said second screen.

ALEXANDER MoLEAN NICOLSON 

